Do you need more pounds or more reps to feel your most fit?

I'm always trying new to find new ways to better my workouts, whether it's mixing up what I do or having different days assigned with different areas. For a past few weeks I've been trying out different ways to see better outcomes. What I've been seeing a lot of progress in abs is when I'm doing my regular reps of 25, but with a heavier weight or something to just make that exercise a little more trickier. With Russian Twists, I'll be wearing my 5 pound foot weights and instead of using a 10 pound ball, I'll use a 12 pound ball and do 4 reps of 25. For my sit ups and crunches, I use an extra 10 pound dumbbell to push up as I'm doing them. Once I get used to them and start getting a little too comfortable with it, I'll add more and more on. I'm always trying to challenge myself, so I will feel like I'm benefitting from the time I've spent at the gym at the end of the week. If you don't already, you should definitely try to add a little weight to your routine to change it up!